1. Field of the Invention
The present invention generally relates to a wireless power transmitter and a wireless power receiver.
2. Description of the Related Art
Mobile terminals such as a mobile phone or a Personal Digital Assistant (PDA) are powered by a rechargeable battery, and a user of a mobile terminal uses a separate charging device to charge the rechargeable battery in order to supply electrical energy to the mobile terminal. In general, the charging device and the battery include respective contact terminals, and a user makes the contact terminals contact each other to electrically connect the charging device with the battery.
However, in the contact type charging method, since the contact terminals are external and are exposed to an outside environment, the contact terminals may be easily contaminated by foreign substances. Accordingly, the battery charging may not be correctly performed. Further, corrosion occurs when the contact terminal is exposed to moisture, making it impossible to achieve a normal battery charging.
In order to solve the above-mentioned problems, a wireless charging or a non-contact charging technology has been recently developed and used for electronic devices.
The wireless charging technology transmits and/or receives electrical power in a wireless manner, and provides a system that can automatically charge the battery by positioning the mobile phone on a charging pad without connecting the mobile phone to a separate charging connector. The wireless charging system is known to the public as being used with a wireless electric toothbrush or a wireless electric razor. The wireless charging technology can provide a waterproof function by charging electronic products in a wireless manner, and can improve portability of the electronic device since a wired charging device is not necessary. It is expected that technologies related to the wireless charging technology will be greatly advanced with the oncoming electric vehicle age.
Such wireless charging technology includes an electromagnetic induction scheme using a coil, a resonance scheme using resonance, and a RF/microwave radiation scheme converting electrical energy into microwaves to transfer the energy via the microwaves.
It is considered up to now that the electromagnetic induction scheme is mainstream, but in the future it is expected that all electronic products will be wirelessly charged, anytime and anywhere, based on recent successful experiments for wirelessly transmitting power to a destination located dozens of meters away, using microwaves.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting power between a first coil and a second coil, by inducing an alternating current in the second coil of a receiving side when a magnetic field is created around the first coil of a transmitter side. The magnetic field is created by applying an alternating current in the first coil of the transmitter side, and the receiver side generates energy by an alternating current being induced in the second coil by the alternating magnetic field, i.e. by a phenomenon referred to as magnetic induction, with the power transmission method using magnetic induction to provide a high energy transmission efficiency.
As the resonance scheme, a system is known in which electrical power is wirelessly transferred using a resonance scheme power transmission principle referred to as coupled mode theory, even when the electronic device is located several meters away from the charging device. This wireless charging system employs a physic concept corresponding to resonance phenomenon akin to vibrating a wine glass at the same frequency of an adjacent tuning fork. Electromagnetic waves having electric energy are resonated instead of sounds. Since the resonated electric energy is directly transferred when there is a device having a resonance frequency and an unused part of the resonated electric energy does not propagate in the air but is reabsorbed in the electromagnetic field, i.e., electromagnetic waves, the resonated electric energy does not influence peripheral devices or a human's body, which is different from other electromagnetic resonance schemes.
In conventional wireless power transmitters and receivers the current carrying metal objects are located around a wireless power transmitter/receiver, the grounding effect of the metal objects may change the high frequency characteristic of a resonator included in the wireless power transmitter/receiver, or may cause the resonator to lose a function or characteristics that transmit or receive electric power at a specific frequency.
An electromagnetic shielding member may be employed in order to solve the above-mentioned problems, but products that include shielding members are more expensive to manufacture. Further, an efficiency of the resonator may be reduced and a resonance frequency thereof may be changed by high frequency characteristics of the shielding member.